1. Field of the Invention
The present invention relates to a thermally printable thermoplastic media and, more particularly, to a thermoplastic material having a leuco-dye, color developer, and a reaction promoter incorporated therein.
2. Description of the Related Art
Since the 1960""s, direct thermal coatings have been applied to paper substrates to produce a receptive media for direct thermal printing. Early applications included meat market marking scales and facsimile machines. Today plain paper faxes are replacing direct thermal printing fax machines, but thermal printing is still dominant in point of purchase receipt printers, scale and variable information label applications, and growing in medical, photo and gaming applications.
Thermal printing processes typically utilize paper which is coated on one surface with a thermal-chromogenic layer comprising a leuco-dye, a color developer and a reaction promoter. Images are formed in the thermal-chromogenic layer by thermal print heads which heat the coated paper to a temperature of 160 to 200 F in selected areas under standard atmospheric conditions. The color developer, when heated, reacts with the leuco-dye to develop a color from the dyes in the thermal-chromogenic layer. This, in turn, causes the formation of images corresponding to the selected areas, i.e., dots generated by the thermal print heads, which are visible against the background color defined by the colored layer.
Typically, paper companies manufacture thermally printable media. However, there is a growing movement and need to replace paper with plastics in several applications. One such application is point of purchase printed sales receipts, such as those printed in grocery stores. Printed receipts are usually handed to a customer and/or in many cases placed in a shopping bag with purchased products. Many retail stores utilize plastic bags and efforts to collect and recycle these bags are becoming widespread. Plastic shopping bags are usually recycled by shredding the bags and re-extruding the shredded bags into pellets to make thick film for disposable trash bags and the like. Paper fiber created by paper receipts left in plastic shopping bags is a serious problem for recyclers since it clogs the screens in the extruder and causes holes to form in the subsequent filmmaking process.
The need and desire to replace paper with plastics has created a need for a thermally printable plastic material. Currently, thermally printable plastic material is produced using the same methods used for thermally printable paper media, i.e., by coating a plastic support sheet with a thermal-chromogenic layer. However, it is both inefficient and costly for paper companies to apply thermal coatings to plastics.
According to a first aspect of the invention, a thermally printable thermoplastic media comprises a thermoplastic material having a thermally activated composition incorporated therein. The thermally activated composition includes a leuco-dye, a color developer, and a reaction promoter. The thermoplastic material may also contain binders and/or fillers. Advantageously, the printable media has a thickness of from about 0.5 to about 1.5 mils to provide a roll with a longer length than a conventional paper roll, thereby increasing the amount of printable media which can be contained on a roll. However, the media may be made thicker for photo and medical applications.
According to a second aspect of the invention a thermally printable thermoplastic media is manufactured by combining a thermoplastic material and a thermally activated composition, melting the combined thermoplastic material and thermally activated composition and forming a film from the combined thermoplastic material and thermally activated composition, typically by extrusion. To prevent pre-imaging or initiation of a thermo-chromogenic reaction from the heat involved in extrusion, the extrusion is preferably carried out in an oxygen-free environment.